Effects of reduced chemical fertilizer application combined with fulvic acid organic fertilizer on soil enzyme activity, bacterial communities, and peanut yield

This study investigated the effects of combining chemical fertilizer and fulvic acid (FA) organic fertilizer on soil enzyme activity, bacterial communities, and peanut yield. Seven treatments were established using the peanut cultivar Shanhua No. 9: no fertilization control (CK), conventional chemical fertilizer (A), 100% FA (B), 20% FA + 80% chemical fertilizer (C), 40% FA + 60% chemical fertilizer (D), 60% FA + 40% chemical fertilizer (E), and 80% FA + 20% chemical fertilizer (F).High-throughput sequencing was used to analyze bacterial community structure, and economic benefits were evaluated. Results showed: (1) Treatments C, D, and E significantly increased catalase activity; treatment F elevated urease activity by 77.67% vs . CK; treatment E enhanced sucrase activity by 60.71%. (2) FA application had a ratio-dependent effect, enhancing bacterial richness and diversity in treatments C and D, while excessive FA substitution in treatment E did not increase richness.(3) Treatment E enriched Proteobacteria and Alphaproteobacteria, promoted Azotobacter and Rhizobium, and decreased Bacillus and Streptomyces abundance. (4) Soil nutrients, pH, salinity, and enzyme activity drove bacterial community shifts. (5) Treatment D yielded 5893.35 kg ha - ¹, exceeding CK and A by 28.52% and 8.39%, with optimal seed weight and kernel recovery. (6) Treatment D showed highest economic return (49,089.3 yuan ha - ¹; input-output ratio 1:13.42). Treatment D (40% FA + 60% chemical fertilizer) optimally enhanced soil biological activity and microbial structure while achieving high yield and efficiency, supporting reduced chemical fertilizer use.